Physics final

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The University of Queensland *

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QCE

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Astronomy

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Dec 6, 2023

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docx

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Rationale Claim : The universe has existed forever and has always looked the same at all times This claim was broken down into main parts: the universe existing forever, and the universe staying the same at all times. In order to start initial research, a broad research question stating, ‘how has the universe changed over time?’ was formulated. Research found that the most widely accepted theory regarding the creation and evolution of the universe is the big bang theory ( Origins of the Universe 101 , n.d.). The big bang theory states that the universe was created around 13.8 billion years ago from an infinitely hot and dense point that inflated and stretched to what it is today(May & Howell, 2023). Although current technology does not allow astronomers to look back to the time of the universe’s birth, evidence such as redshift of light help support the big bang theory (Howell & Dobrijevic, 2022). Although there are many other pieces of evidence for the big bang theory, redshift gives evidence that the universe is constantly expanding and moving away from a central point ( Big Bang Theory , n.d.). Therefore, redshift became the focus of the research question shown below. Research question How does redshift of light give evidence that the universe is constantly changing? Evidence In 1929, a scientist by the name of Edwin Hubble discovered that there were other galaxies beyond our own and the universe was expanding at a constant rate. This constant expansion of the universe was seen through the redshift of light. Redshift is comparable to the baking of a blueberry muffin. The mixture spreads as the muffin bakes and rises, scattering the blueberries. If the batter doubles in size and two blueberries are a centimetre apart, the space between them will also double. When the muffin is baked, the two blueberries that were previously separated by a centimetre will now be two centimetres apart. Similarly, it is expected in a universe that is expanding everywhere, distant galaxies are moving away from us quicker than nearby galaxies. Redshift occurs when the light waves that are being emitted become more stretched. This occurs due to the observed object’s light waves being stretched due to the universe expanding, causing the frequency to decrease and wavelength increase ( Astronomical Redshif , n.d.). The increase in wavelength causes the light that reaches the observer to be shifted more towards the red end of the electromagnetic spectrum, thus redshift occurs (shown in figure 1).
Figure 1: Representation of redshifted light ( Astronomical Redshif , n.d.) Hubble created a law stating that the distance of a star and the speed of recession (redshift) were directly proportional to each other. The law is stated below: v = H 0 D v = recessional velocity (redshift) H 0 = Hubble’s constant (70km/s/MPS) D = proper distance Hubble’s constant was discovered by comparing distances to galaxies to their redshift ( Hubble’s Law | Cosmic Redshif | Western Washington University , n.d.)(shown in figure 2). This allowed Hubble to graph multiple galaxies against each other and clearly see the relationship between redshift and distance. Figure 2: Comparison of galaxies to their redshift and distance ( Hubble’s Law | Cosmic Redshif | Western Washington University , n.d.) If the universe has always looked the same at all times, there would be no relationship between distance and recessional velocity (redshift) ( Ian.S , 1997). However, if the universe is constantly expanding, it would be expected that there would be a relationship between distance and recessional velocity (redshift) (shown in figure 3). Figure 3: Relationship between redshift and distance (Dictionary of Astronomy, 1997) Hubble’s law and the discovery of redshift are proof of the ever-changing and ongoing expansion of the universe, disproving the claim that the universe has always looked the same at all times.
Interpretation The research shows that the redshift is proof for the universe constantly expanding, and that the redshift of a light source and the distance are directly proportional. Quality of Evidence The two main pieces of evidence came from an article published by the Physics and Astronomy department of the University of Iowa, and the Dictionary of Astronomy by Ian Ridpath. The source of information covering the redshift came from Iowa University which is rated 131 out of 1148 American Universities (top 15%) based on 66 evaluation metrics ( Physics Schools , 2022). Therefore it is assumed that the data and information released on the university website is credible and that the information regarding the redshift is reliable. A limitation within the research was the age of the Dictionary of Astronomy by Ian Ridpath which impacts its reliability. Although the concept of redshift was discovered in 1929, there may be new findings about redshift that might not be found in the book which was published in 1997, possibly impacting the reliability of the findings. Furthermore, a limitation within all sections of the evidence, is that the majority of the research for the evidence came from only two sources. Although both sources are considered reliable, this still would have impacted the validity, due to the lower number of sources. A larger number of sources that corroborate information regarding redshift would have increased the validity of the findings. Conclusion and Evaluation To encapsulate the evidence provided in this report, the research question ‘how does redshift of light give evidence that the universe is constantly changing?’ can be answered confidently. It was found that the redshift of light gives evidence that the universe is constantly expanding and that the relationship between redshift and distance are directly proportional. Redshift occurs due to the light coming from an observed galaxy being shifted to the red end of the electromagnetic spectrum caused by the expansion of the universe stretching the light waves that reach the observer. The claim, ‘The universe has existed forever and has always looked the same at all times’ can be partially disproved as not all areas of the claim have been addressed, seen in the neglection of addressing the creation of the universe. In order to better address the claim and increase the reliability and validity of the findings, the following improvements and extensions should be considered in the future. Improvements and extensions To address the limitations of the findings, the following improvements and extensions should be considered in the future: Improvement: Finding more sources that corroborate the finding that redshift proves the constant expansion of the universe, as some sources may include inaccurate findings or biases. Thus, including more reliable sources would improve the validity. Improvement: Finding more recent data that discuss recent findings of redshift and Hubble’s constant. This would improve the reliability and validity of the findings as they would be more recent and more likely to be more accurate, as opposed to being nearly 100 years old.
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